The invention relates generally to desalination systems and methods for water recovery. More particularly, this invention relates to desalination systems and methods for removal of hardness ions for product water recovery.
In industrial processes, large amounts of wastewater, such as aqueous saline solutions are produced. Generally, such wastewater is not suitable for direct consumption in domestic or industrial applications. In view of the limited eligible water sources, it is desirable to recover eligible water from liquid streams, such as wastewater, seawater or brackish water.
Typically, due to continuous operation, and stable and relatively higher quality of product water, electrodeionization (EDI) apparatuses have been employed for processing such liquid streams, for example for production of pure water. Generally, the EDI apparatuses use conventional electrodialysis systems filled with ion exchange resin beads to process the liquid streams. However, during operation, the EDI apparatuses have a hardness tolerance for the liquid streams to be processed. For example, the hardness tolerance of the EDI apparatuses is about less than 1 ppm, which may need rigorous pretreatment of the liquid streams to decrease the hardness therein before the liquid streams are introduced into the EDI apparatus.
There have been attempts to pretreat the liquid streams to decrease the hardness therein. For example, two stages of reversal osmosis (RO) apparatuses are employed. However, due to employment of two stages of the reversal osmosis apparatuses, the system cost may be higher for decreasing the hardness in the liquid streams.
Therefore, there is a need for new and improved desalination systems and methods for removal of hardness ions for water recovery.